1. Field of the Invention
The present invention concerns a fast, dynamic scale and a method to control a fast, dynamic scale that allow rapid weighing of general cargo, for example, mail pieces. The invention is suitable for use in mail processing systems that have an increased throughput.
2. Description of the Prior Art
In mail processing various solutions are known in the field of dynamic weighing. The companies Neopost and Pitney Bowes offer table devices for approximately horizontal transporting systems, wherein the mail pieces are transported lying flat on the back side thereof so that a franking stamp can be applied to the front side of the mail pieces.
From European Patent EP 974 819 B1 a device is known to weigh moving mail goods, in particular to weigh mail pieces (letters) arranged standing on edge. A transport belt driven by a motor runs on track rollers over a weighing plate that is equipped with a guide wall to guide the mail pieces. The guide wall is equipped to guide the mail pieces and is tilted at an angle of 108° relative to the table plate.
The mail pieces—tilted onto their front sides—slide further along the guide wall while the approximately horizontally-arranged transport belt is moved further, on which transport belt the mail pieces are transported, standing on edge. Mail pieces are, for example, post cards, letters in envelopes and other mail goods up to 20 mm in thickness. The throughput in the latter cited system amounts to approximately 50 letters per minute with dynamic weighing of the mail goods. The throughput of a franking machine is determined from the number of letters per time unit and amounts at most to 150 letters per minute. At a given transport speed and a letter separation from the leading letter edge of one enveloped letter to the leading letter edge of the next enveloped letter (edge to edge), the throughput results from the quotient of the transport speed and the letter spacing. The motor, the transport belt with track rollers and the weighing plate with guide wall load a weighing cell. On a weighing cell the weighing plate with the transport belt and the track rollers as well as a first motor are arranged so that the weighing cell is loaded with an initial load (tare weight). A first sensor is arranged at the intake of the weighing unit, this sensor emitting a first signal to a control unit that starts the weighing process for a letter B. Moreover, a second sensor is provided at the outlet of the of the weighing unit, this second sensor emitting a second signal to a control unit which generates a communication that a following letter Bn, which follows the letter B, can be supplied. The aforementioned components form the dynamic scale that is operated together with a franking machine of the Jetmail® type in a franking system from the assignee, which together determine the throughput of mail pieces.
To increase throughput by shortening the interval between the letters, from EP 2017589 A2 (=US 20090008859 A1) a system transporting the letters approximately horizontally is known in which at least two weighing units are arranged in succession. Short letters can be weighed successively with a short interval by means of a first weighing unit because the latter is adapted in terms of its length to the length of the short letters. Given long letters the weighing result is a superposition of the weighing results of both weighing units. The higher cost relative to a system with only a single weighing unit is disadvantageous. The connection of multiple weighing units in series makes a markedly higher computing cost necessary in the calculation of the weight values, which can be time-critical. Slippage/synchronization problems can occur between the weighing units that can lead to impacts that can affect the weighing result.
An additional solution to increase throughput exists in a parallel arrangement of two weighing units is known from EP 2,065,686 A1 (=US 20090139777 A1). The connection of two weighing units in parallel entails the problem of the markedly increased space requirement due to the two units to control the letter flow, a markedly increased control expenditure and higher costs. Moreover, additional devices are necessary to divide and merge the letter flow before and after the scale, which further drives up the space requirement.
A franking system from Francotyp-Postalia GmbH include at least one automatic feed station, a dynamic scale and a franking machine downstream in the mail flow. For the franking machine of the Centormail® type a transport system is used in which mail pieces standing on edge are transported in succession. Given mail pieces such as letters, a letter range of letter lengths from 140 mm to 353 mm can be processed. Letters in the C6 length format thus have a median letter length of 229 mm. Customer requirements for a higher throughput of the franking system with the Centormail® franking machine make it necessary to either increase the transport speed for mail pieces (in particular letters) in a system or to reduce the interval between the letters. However, the length of the weighing unit that is required in practice can only be determined only by testing (experimentation).